Ahodges/documentation/for662

Added procedures for adding posts, responses, and comments in discussion topics on the Discussion page and in the courseware. Also added contextual information ("Anatomy") for students.
Decap and de-bold **Display Name**, **Category**, and **Subcategory** since these aren't proper nouns, unless you want to say something like "The value in the **Display Name** field." (See https://docs.google.com/a/edx.org/document/d/1MSGxuZOVzca56V-N6AnE7LTAuNuwYp6QC_-Rlv3fTNQ/edit#bookmark=id.woypajkt76c.)